Emulsions - Instability mechanisms

4 important questions on Emulsions - Instability mechanisms

Emulsion stability is a combination of 2 things

  1. Emulsion formation --> smaller proteins diffuse quicker to interface than larger proteins
  2. Interfacial thickness --> thicker interface prevents coalescence. Larger proteins wanted

Which main process cause the instability of emulsions?

  • Flocculation --> at high concentrations, droplet may form a network and a gel
  • Coalescence --> during homogenisation, but not during storage
  • Creaming or sedimentation --> oil and air are lighter, so they cream
  • Ostwald ripening (for emulsions) and disproportionation (for foams) --> polydisperse size-distribution needed, fluid inside droplet is slightly soluble in continuous phase

Does Ostwald ripening occur as much in emulsions as disproportionation in foams?

No. Oils have a fairly low solubility in water. So it has only a minor effect on emulsion stability.
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Which 3 forces act in sedimentation/creaming?

  1. Gravitational force
  2. Buoyancy force --> opposite to the direction of the gravitational force
  3. Friction force --> friction that acts on the moving particle, direction opposite of the direction to which the particle moves

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